Encode interpreter::SourcePositionTable as variable-length ints.

test/unittests/interpreter/source-position-table-unittest.cc

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/v8.h"
+
+#include "src/interpreter/source-position-table.h"
+#include "test/unittests/test-utils.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+class SourcePositionTableTest : public TestWithIsolateAndZone {
+ public:
+  SourcePositionTableTest() {}
+  ~SourcePositionTableTest() override {}
+};
+
+// Some random offsets, mostly at 'suspicious' bit boundaries.
+static int offsets[] = {0,   1,   2,    3,    4,     30,      31,  32,
+                        33,  62,  63,   64,   65,    126,     127, 128,
+                        129, 250, 1000, 9999, 12000, 31415926};

[Yang, 2016/02/17 19:54:51]

Since we are encoding the delta, these are not really suspicous, are they? Could
we have a few offsets where the difference to the last one is some power of 2?

Also, we don't really test negative delta for source positions.

[vogelheim, 2016/02/18 13:06:09]

I disagree. Your feedback is correct for the first two tests, but the
EncodeAscending test handles both of those issues. I actually did that on
purpose, so that the different unit tests would test different things. E.g.
EncodeStatement succeeding but EncodeAscending failing would likely indicate an
issue with negative numbers and/or bit the bit boundaries.

[Yang, 2016/02/19 08:28:02]

I see. Ok.

+
+TEST_F(SourcePositionTableTest, EncodeStatement) {
+  SourcePositionTableBuilder builder(isolate(), zone());
+  for (int i = 0; i < arraysize(offsets); i++) {
+    builder.AddStatementPosition(offsets[i], offsets[i]);
+  }
+
+  // To test correctness, we rely on the assertions in ToSourcePositionTable().
+  // (Also below.)
+  CHECK(!builder.ToSourcePositionTable().is_null());
+}
+
+TEST_F(SourcePositionTableTest, EncodeExpression) {
+  SourcePositionTableBuilder builder(isolate(), zone());
+  for (int i = 0; i < arraysize(offsets); i++) {
+    builder.AddExpressionPosition(offsets[i], offsets[i]);
+  }
+  CHECK(!builder.ToSourcePositionTable().is_null());
+}
+
+TEST_F(SourcePositionTableTest, EncodeAscending) {
+  SourcePositionTableBuilder builder(isolate(), zone());
+
+  int accumulator = 0;
+  for (int i = 0; i < arraysize(offsets); i++) {
+    accumulator += offsets[i];
+    if (i % 2) {
+      builder.AddStatementPosition(accumulator, accumulator);
+    } else {
+      builder.AddExpressionPosition(accumulator, accumulator);
+    }
+  }
+
+  // Also test negative offsets:
+  for (int i = 0; i < arraysize(offsets); i++) {
+    accumulator -= offsets[i];
+    if (i % 2) {
+      builder.AddStatementPosition(accumulator, accumulator);
+    } else {
+      builder.AddExpressionPosition(accumulator, accumulator);
+    }
+  }
+
+  CHECK(!builder.ToSourcePositionTable().is_null());
+}
+
+TEST_F(SourcePositionTableTest, EncodeRevert) {
+  SourcePositionTableBuilder builder(isolate(), zone());
+
+  int accumulator = 0;
+  for (int i = 0; i < arraysize(offsets); i++) {
+    accumulator += offsets[i];
+    builder.AddStatementPosition(accumulator, accumulator);
+
+    // Every other position is reverted. Among these, every other position
+    // is reverted with the same bytecode offset.
+    if (i % 4 == 1) {
+      builder.RevertPosition(accumulator);
+    } else if (i % 4 == 3) {
+      builder.RevertPosition(accumulator + 1);
+    }
+  }
+
+  CHECK(!builder.ToSourcePositionTable().is_null());
+}
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8